Microfluidic devices, as understood herein, include fluidic devices over a scale ranging from microns to a few millimeters, that is, devices with fluid channels the smallest dimension of which is in the range of microns to a few millimeters, and preferably in the range of from about 10's of microns to about 1.5 millimeters. Partly because of their characteristically low total process fluid volumes and characteristically high surface to volume ratios, microfluidic devices, particularly microreactors, can be useful to perform difficult, dangerous, or even otherwise impossible chemical reactions and processes in a safe, efficient, and environmentally-friendly way. Such improved chemical processing is often described as “process intensification.”
Process intensification is a relatively new emphasis in chemical engineering which has the potential to transform traditional chemical processing, leading to smaller, safer, and more energy-efficient and environmentally friendly processes. The principal goal of process intensification is to produce highly efficient reaction and processing systems using configurations that simultaneously significantly reduce reactor sizes and maximize mass- and heat-transfer efficiencies. Shortening the development time from laboratory to commercial production through the use of methods that permit the researcher to obtain better conversion or selectivity is also one of the priorities of process intensification studies. Process intensification may be particularly advantageous for the fine chemicals and pharmaceutical industries, where production amounts are often smaller than a few metric tons per year, and where lab results in an intensified process may be relatively easily scaled-out in a parallel fashion.
Process intensification consists of the development of novel apparatuses and techniques that, relative to those commonly used today are expected to bring very important improvements in manufacturing and processing, substantially decreasing equipment-size to production-capacity ratio, energy consumption and/or waste production, and ultimately resulting in cheaper, sustainable technologies. Or, to put this in a shorter form: any chemical engineering development that leads to a substantially smaller, cleaner, and more energy efficient technology is process intensification.
The present inventors and/or their colleagues have previously developed various microfluidic devices useful in process intensification and methods for producing such devices. These previously developed devices include apparatuses of the general form shown in prior art FIG. 1. FIG. 1, not to scale, is a schematic perspective showing a general layered structure of certain type of microfluidic device. A microfluidic device 10 of the type shown generally comprises at least two volumes 12 and 14 within which is positioned or structured one or more thermal control passages not shown in detail in the figure. The volume 12 is limited in the vertical direction by horizontal walls 16 and 18, while the volume 14 is limited in the vertical direction by horizontal walls 20 and 22.
The terms “horizontal” and “vertical,” as used in this document are relative terms only and indicative of a general relative orientation only, and do not necessarily indicate perpendicularity, and are also used for convenience to refer to orientations used in the figures, which orientations are used as a matter of convention only and not intended as characteristic of the devices shown. The present invention and the embodiments thereof to be described herein may be used in any desired orientation, and horizontal and vertical walls need generally only be intersecting walls, and need not be perpendicular.
A reactant passage 26, partial detail of which is shown in prior art FIG. 2, is positioned within the volume 24 between the two central horizontal walls 18 and 20. FIG. 2 shows a cross-sectional plan view of the vertical wall structures 28, some of which define the reactant passage 26, at a given cross-sectional level within the volume 24. The reactant passage 26 in FIG. 2 is cross-hatched for easy visibility and includes a more narrow, tortuous passage 30 followed by a broader, less tortuous passage 32. Close examination of the narrow, tortuous passage 30 in FIG. 2 will show that the tortuous passage 30 is discontinuous in the plane of the figure. The fluidic connections between the discontinuous sections of the tortuous passage shown in the cross section of FIG. 1 are provided in a different plane within the volume 24, vertically displaced from plane of the cross-section shown in FIG. 2, resulting in a passage 30 that is serpentine and three-dimensionally tortuous. The device shown in FIGS. 1 and 2 and related other embodiments are disclosed in more detail, for example, in European Patent No. EP 01 679 115, C. Guermeur et al. (2005). In the device of FIGS. 1 and 2 and similar devices, the narrow, more tortuous passage 30 serves to mix reactants while an immediately subsequent broader, less tortuous passage 32 follows the passage 30 and serves to provide a volume in which reactions can be completed while in a relatively controlled thermal environment.
Although good performance has been obtained with devices of this type, in many cases even exceeding the state of the art for a given reaction, it has nonetheless become desirous to improve upon the thermo- and fluid-dynamic performance of such devices. In particular, it is desirable that the heat exchange performance of such devices be improved while simultaneously approximately maintaining at the same level or even decreasing the pressure drop caused by the device, while increasing mixing performance and throughput.
In U.S. Pat. No. 6,935,768 (corresponding to DE 10041823), “Method and Statistical Micromixer for Mixing at Least Two Liquids,” successive expansion chambers 6 are spaced apart along a narrow channel 5, (see FIG. 2) for the purpose of generating standing vortices in the expansion chambers as an aid to mixing.